1575-85; < Latindēsultōrius pertaining to a dēsultor (a circus rider who jumps from one horse to another), equivalent to dēsul-, variant stem of dēsilīre to jump down (dē-de- + -silīre, combining form of salīre to leap) + -tōrius-tory1

1580s, "skipping about," from Latin desultorius "hasty, casual, superficial," adjective form of desultor (n.) "a rider in the circus who jumps from one horse to another while they are in gallop," from desul-, stem of desilire "jump down," from de- "down" (see de-) + salire "to jump, leap" (see salient (adj.)). Sense of "irregular, without aim or method" is c.1740. Related: Desultorily; desultoriness.